Urethane foam that is orthogonally reinforced with filaments is an effective cryogenic insulation. One use of such insulation is in insulating compartments or holds of marine vessels used to transport liquid natural gas. Transporting natural gas in its liquid state (at cryogenic temperatures) is preferable to transporting it in its gaseous state since it is reduced in volume approximately 600 times.
In one form, a metal storage tank is spaced from the hull of the vessel and insulation is applied to the inside of the tank. The Z fibers in the foam insulation planks are bonded to sheets of plywood bolted to the tank, or the fibers may be bonded directly to the tank inner walls. The layered X--Y fibers of adjacent planks are bonded together to form a unitary contiguous insulation blanket that serves to contain the liquid natural gas.
Heretofore, 3D reinforced foam insulation was made in block form in intermittent steps. One such method is disclosed in U.S. Pat. No. 3,778,429 which issued to C. R. Lemons on Dec. 11, 1973 for Fabrication of Three-Dimensional Reinforced Foam Insulation Blocks. By this method, reinforcing filaments are attached to cardboard frames or strips which are subsequently stacked and arranged over a pan in which the raw foam batter is placed. The foam then rises through the filamentary array. After the foam is cured, the cardboard is cut away (and discarded) and the remaining foam block is bonded to similar blocks when used as an insulation material. The non-productive cardboard frames and the batch process method of arraying the filaments and foaming are expensive, time-consuming and wasteful of material.
U.S. Pat. No. 3,972,554 to Muskat et al., discloses a continuous method of producing fiber reinforced foam pads by impregnating batts of randomly arranged fibers with resin. Disclosures of a similar nature are found in U.S. Pat. Nos. 3,273,978 to Paul and 3,867,494 to Rood, the latter patent disclosing orientation of the fibers in layers. In the latter case, the fibers have a tendency to deteriorate or exfoliate along the planes of reinforcement.
However none of the above patents teaches continuous production of a foamed array of reinforcing fibers which are oriented in the X, Y and Z direction according to the present invention.